The phosphoinositide 3-kinase (PI3K) signaling pathway plays a central role in promoting neuronal survival and differentiation. PDK1 is a crucial master kinase that, in response to PI 3-kinase activation, switches on a number of AGC-kinase family members including PKB/Akt. Activation of Akt by PDK1 relies on the interaction of the PH domains present on both kinases with PtdIns(3,4,5)P3, the PI 3-kinase product. Crystal structure high-resolution of the PDK1 PH-domain allowed the design of a specific point mutation, Lys 465 to Glu, impairing the interaction of the PH-domain with PtdIns(3,4,5)P3. The PDK1K465E/K456E mice were shown to be viable but smaller, with a modest reduction in Akt activity compared with the wild type mice. By contrast, other PDK1 target such as RSK, S6K or SGK isoforms remained unaffected. Our former studies have indicated that neuronal survival was not compromised in the PDK1K465E/K465E mice, although activation of Akt was obviously reduced. Even after treated with the Akti-1/2 inhibitor, cortical neurons were still surprisingly capable to survive. Regarding this, I proposed that Akt3 plays key role in regulating neuronal survival. The results of my study indicate that the PKB/Akt activation in cortex was less reduced than in insulin responsive tissues in the PDK1K465E/K465E mice. I further analyze the activity of different Akt isoforms, and I found that PKBγ/Akt3 activity was preserved compared with PKBα/Akt1 or PKBβ/Akt2 in the PDKK465E/K465E mice, and also that the proportion of Akt3 phosphorylation at the PDK1 site is much higher in neurons than in other tissues in the PDK1K465E/k465E mice. The PKBβ/Akt2 only accounted for a small fraction of the total PKB/Akt activity in cortical neurons, which implies unimportant role in regulating the neuronal survival. Furthermore, The data from Akt shRNA interference and Hoechst assays demonstrate that the percentage of apoptotic cells was increased by Akt1 and Akt3 shRNAs infection in cortical neurons In the PDK1K465E/K465E mice, whereas Akt2 down-regulation had no significant effects on neuronal apoptosis. Here I proposed a model that the neuronal survival was regulated by PKB/Akt isoforms in a quantitative manner. Because of the high proportion of Akt phosphorylation at Thr 8/9 sites, Akt1 and Akt3 might play more important roles than Akt2 in neuronal survival. Besides this, I also uncovered a novel mechanism in the activation of PKB/Akt in the PDK1K465E/K465E mice, In which PDK1 can take advantage of the docking site mechanism to activate Akt, in spite of the absence of PtdIns(3,4,5)P3 binding.